The present invention relates to a power generation system for providing power to an electric power system, and more specifically to a wind power generation system.
The doubly-fed generator (wound-rotor induction generator) used for a power generation system can output an AC voltage of the same frequency as the system frequency on the stator side by the power converter exciting the rotor coil at a slip frequency, thereby variably controlling the number of rotations. Furthermore, the power generation system using a doubly-fed generator can require reduced capacity of power converter as compared with the capacity of a generator.
However, when a voltage drops due to a ground fault in an electric power system, the doubly-fed generator operates to supply a current to a faulty point. At this time, an overcurrent is induced in the secondary coil, and an overcurrent passes through an exciting power converter connected to the secondary side. Therefore, to stand the overcurrent, the element capacity of the power converter is increased to the rating equal to or more than that of the generator, or an alternating current reactor for short-circuiting the secondary coil, etc.
Conventionally, a doubly-fed generator is mainly provided for a large wind power generation system and a power converter is temporarily stopped in a long power failure in a system, and is activated again after the system voltage is recovered to the normal condition. For example, the JP-A-11-18486 discloses an example of a power conversion device for a conventional doubly-fed generation system.